Echinacea: Cure for the Common Cold?

By Shannon Bell ‘00

Lining the aisles of drug stores across the country is evidence of our eternal battle with that annoying intruder arriving uninvited about twice a year: the ever-lurking cold virus. There are literally hundreds of drugs that claim to stop the runny noses, sneezing, coughing, nasal congestion, headaches, and sore throats that usually surface a couple days after a cold virus has entered our bodies.

In recent years, another bottle has appeared in the drug store aisles: Echinacea purpurea. Also known as the purple coneflower, this plant is indigenous to the eastern and central United States. Although it is reported that the Native American Plains Indians used it medicinally more than any other plant and that it was used widely in the early 20^th Century, it fell from use after the advent of antibiotics. The Europeans, however, noted its value and have cultivated and used it since the 1930s. It has not been until recently that Echinacea has come back into favor as a medicinally valuable plant. Today, it is so common that one can easily find a preparation in a grocery store almost anywhere in the United States. Many people use this plant for its supposed immunostimulatory effects. I even use it in the winter, especially near finals time when my stress level is high, sleep level is low, and I am incredibly susceptible to unwanted viral intruders. But does this plant really improve the immune system’s function?

The Immune System

There are two divisions of the immune system: innate, or non-specific immunity, and aquired, or specific immunity. The innate immune system involves the activation and stimulation of cells that unselectively phagocytize, or engulf, any foreign invaders, while the acquired immune system differs in that it produces antibodies. Antibodies allow for specificity in killing foreign invaders and also create memory so that the next time the alien antigen appears, the immune system will be able to quickly destroy it.Echinacea is reported to be an immunostimulant of the innate immune system, but because the innate immune system is required in order for the activation of the acquired immune system, Echinacea ultimately helps in both of these systems. Macrophages and monocytes are cells in the innate immune system whose major role is the phagocytosis of foreign invaders and the subsequent presentation of the foreign antigen to the B and T lymphocytes of the acquired immune system. Natural killer cells and polymorphonuclear leukocytes are also part of innate immunity. Both of these cells destroy foreign antigens, either through phagocytosis or through causing cell lysis.

Clinical Evidence

The Department of Family Medicine at the University of Wisconsin-Madison conducted an intensive review of thirteen clinical trials that tested the effects of Echinacea in treating upper respiratory infections (URIs). In order to be reviewed, the clinical studies had to meet very strict criteria set by the researchers. Randomization, blinding, validity and clinical relevance of measurements, the degree to which the treatment and placebo were indistinguishable, inclusion and exclusion criteria, power, and the appropriateness of the conclusions drawn based upon the presented data were all criteria the researchers considered when choosing the studies they were going to include.

There were nine treatment trials and four prevention trials which fit the selection conditions. It was found that eight of the treatment trials, (in which patients took Echinacea when cold symptoms first appeared and then for the following eight days) the experimental groups had a significantly shorter duration and milder symptoms of the cold viruses than the placebo groups. The one study whose findings did not agree with the other eight studies used a dose of Echinacea that may have been too low to be effective. However, the four trials that tested the preventative effects of Echinacea on cold viruses were not conclusive. Thus, this review suggests that Echinacea is beneficial in the early treatment of URIs, but does not suggest that the prolonged use of this plant aids in the prevention of URIs.

Mechanism of Action

The Department of Anatomy and Cell Biology at McGill Univeristy in Montreal conducted a study in which they determined the effects of Echinacea on the immune cells of normal mice. After administering a potent extract of Echinacea root daily for two weeks, it was found that the numbers of natural killer cells and monocytes were significantly increased in both the spleen and bone marrow after only one week of treatment. All other hemopoitic and immune cell populations in these two organs remained constant throughout the two-week study. From these findings, one can infer that at least one way in which this herb increases innate immunity is through the stimulation of new cell production.

Burger, et. al. have suggested another mechanism of action through their study of Echinacea’s effects on in vitro cytokine production in macrophages. Cytokines are important chemical substances that have many different roles in immunity, one very important role being that of "turning on" the acquired immune system by activating T cells. Commercial preparations of Echinacea were tested at various concentrations, ranging from 10 micrograms/ml to 0.012 microgram/ml. It was found that macrophages cultured in concentrations of the plant even as low as 0.012 microgram/ml produced significantly higher levels of cytokines than unstimulated cells.

Another study at the University of Florida in Gainesville led by Susan Percival has suggested yet another effect that Echinacea has on the cells of the immune system. Researchers administered a commercial preparation of the herb, which contained 150 mg of active ingredients. On the first and last days of the study, researchers drew blood from the subjects and removed the neutrophils for further study. When there is an infectious agent in the body, these cells respond by emitting a "superoxide anion," which is a biologically damaging and highly reactive oxidant that works to kill the invader. They found that upon stimulating the neutrophils in a way that mimics an encounter with foreign antigens, these cells produced three times the amount of superoxide anion than the amount that the cells collected at the beginning of the study did. Thus, not only has Echinacea been found to increase the production of immune cells themselves, but also to increase the output of some of these cells.

The specifics of how Echinacea works to stimulate these immune activities is not yet understood, and the exact chemicals that have these effects are not presently known, but this area is currently under intensive study. Two high-molecular-weight polysaccharides that have been found to have immunostimulatory effects have been isolated from the aerial parts of the plant. They are 4-O-methylglucuronoarabinoxylan and acid rhamnoarabinogalactan. In the squeezed juice of the flowers, acidic arabinogalactan is the main active component. This polysaccharide has been found to increase phagocytosis and the release of interferon and tumor necrosis factor. However, polysaccharides’ immunostimulatory effects have only been shown in vitro or after administration parenterally. Thus, more studies need to be conducted to conclude whether or not oral administration elicits the same responses.

Dosage

Recommended dosage of Echinacea is dependent upon the potency of the preparation being taken. A typical recommendation of a typical American hydroalcoholic preparation is to take from fifteen to thirty drops (0.75 to 1.5 ml) two to five times a day. The German Commission E recommends taking a preparation which includes 900 mg of crude drug (from the root fluid extract) and 6 to 9 mg. of the pressed juice.

Side Effects

It is important to note that although many people (including myself until now) take this herb to prevent URIs, there is no evidence that it is effective in this use, and may even be harmful. Contrary to popular belief, Echinacea should not be taken on a regular basis. As Susan Percival of the University of Florida has found through her research, Echinacea’s ability to increase the immune system’s functions also increases the output of free radicals. Free radicals are important in destroying microorganisms, but they are not selective in what tissues they attack. Thus, they can also be extremely destructive to our organs.

Conclusion

From the studies and research summarized here, it is apparent that Echinacea is a useful herb in helping to bolster the immune system when the first signs of a virus set in. It has been shown to have the greatest benefits when it is taken at the beginning of a cold, and helps to lesson the duration and symptoms of the sickness. However, research reveals that this herb should not be taken continually in hopes that it will prevent sicknesses because there may be destructive side-effects to body tissues as a result of the heightened number of free radicals in the system.